This invention relates to an air bag actuator, and particularly to a two-stage ignition type air bag actuator which has two inflators, and ignites them in a predetermined sequence and at a predetermined time interval depending on a collision event.
FIG. 1 is a diagram showing the configuration of the conventional air bag system.
Referring to FIG. 1, a reference numeral 101 denotes a mobile battery, 102 an ignition switch, 103 a driver-side air bag, 104 an igniting device for the first-stage inflators of the driver-side air bag, 105 an igniting device for the second-stage inflators of the driver-side air bag, 106 a passenger-side air bag, 107 an igniting device for the first-stage inflators of the passenger-side air bag, 108 an igniting device for the second-stage inflators of the passenger-side air bag, 109 an air bag control unit, 110 a DC-DC converter, 111 a backup capacitor, 112 a mechanical acceleration switch, 113 an acceleration sensor, 114 an ignition judging means, 115 and 116 driving transistors for the first-stage inflators of the driver-side air bag 103, 117 and 118 driving transistors for the second-stage inflators of the driver-side air bag 103, 119 and 120 driving transistors for the first-stage inflators of the passenger-side air bag 106, and 121 and 122 driving transistors for the second-stage inflators of the passenger-side air bag 106.
Now, the operation of the air bag system shown in FIG. 1 will be described.
When the ignition switch 102 is closed, the DC power outputted from the mobile battery 101 is boosted in the DC-DC converter 110 to charge the backup capacitor 111.
If a collision occurs, the mechanical acceleration switch 112 closes while a large negative acceleration caused by the collision is acting. Further, the ignition judging means 114 receives an acceleration signal outputted from the acceleration sensor 113, and if it judges that a collision has occurred, it turns ON the driving transistors 115, 116, 119, and 120 to ignite the first-stage inflators of the driver-side air bag 103 and the passenger-side air bag 106. This allows a current necessary for ignition to pass through the igniting device 104 and the igniting device 107 to respectively ignite the first-stage inflators of the driver-side air bag 103 and the passenger-side air bag 106, and the driver-side air bag 103 and the passenger-side air bag 106, beginning to inflate them to an appropriate size. After the first-stage inflators are ignited, if a predetermined condition is fulfilled, the ignition judging means 114 turns ON the driving transistors 117, 118, 121, and 122 to further ignite the second-stage inflators of the driver-side air bag 103 and the passenger-side air bag 106. This allows a current necessary for ignition to pass through the igniting device 105 and the igniting device 108 to respectively ignite the second-stage inflators of the driver-side air bag 103 and the passenger-side air bag 106, and the driver-side air bag 103 and the passenger-side air bag 106, inflating them to the maximum.
The above two-stage ignition type air bag system is described, for instance, in JP 11-263188 A and determination as to whether or not the second-stage inflators should be ignited after the first-stage inflators are ignited, for instance, through comparison with variable characteristic data of various negative accelerations obtained by experiments or computer simulations.
Further, the mechanical acceleration switch 112 is provided to prevent a current from passing through inflators even if driving transistors malfunctioned, and to inhibit the ignition of the inflators due to the malfunction. Such mechanical acceleration switch is described, for instance, in JP 09-211023 A and the mechanical acceleration switch described in this publication has a structure in which a weight is moved by the so-called collision acceleration due to a collision to close the switch, and, when the acceleration disappears, the weight returns to its predetermined position by a spring force to open the switch.
Since the conventional two-stage ignition type air bag system is configured as described above, in which the second-stage inflators are ignited, with a predetermined time delayed after the first-stage inflators are ignited, if the negative acceleration at the ignition of the second-stage inflators is lower than a predetermined one, then the mechanical acceleration switch opens, disabling the supply of an ignition current from the backup capacitor. Likewise, where it is necessary to further inflate the air bag, the second-stage inflators cannot be ignited.
Moreover, to avoid the arising of the above problems, if the mechanical switch is omitted, the fail-safe function for electrical malfunction is lost as a necessary consequence.
This invention has been made to solve the above problems, and an object thereof is to provide a air bag actuator incorporating a fail-safe function for electrical malfunction, and enabling the second-stage inflators to be forcibly ignited, regardless of whether the mechanical acceleration switch is opened or closed.
The air bag actuator of this invention comprises power supply means for supplying a current necessary for igniting the inflators; a mechanical acceleration switch, which is disposed between the common junction of a first-stage igniting device provided for every one or more first-stage inflators and a second-stage igniting device provided for one or more second-stage inflators, and opens or closes depending on the acceleration of a vehicle; one or more first switching means connected in series with the first-stage igniting device for every the first-stage igniting device; one or more second switching means connected in series with the second-stage igniting device for every the second-stage igniting device; an acceleration sensor for detecting how far the acceleration is applied to the vehicle, and for outputting a signal corresponding to the acceleration; an ignition judging means, connected to the control terminals of the first switching means and the second switching means for controlling ON-OFF of the first switching means and the second switching means in response to the signal inputted from the acceleration sensor; and a forcible ignition means, disposed between the common junction of the igniting devices and the power supply means in parallel with the mechanical acceleration switch, for electrically connecting or disconnecting the common junction of the ignition means and the power supply means in response to the signal from the ignition judging means.
Thus, upon receipt of ignition instructions for the second-stage inflators from the ignition judging means, power can be supplied from the power supply means, regardless of whether the mechanical acceleration switch is opened or closed, so if the second-stage inflators need to be ignited, it ensures reliably ignition.
The air bag actuator of this invention comprises, in the forcible ignition means; forcible ignition switching means disposed between the common junction of the igniting devices and the power supply means in parallel with the mechanical acceleration switch; closure detecting means for detecting the mechanical acceleration switch is opened or closed, and for, upon the closing of the mechanical acceleration switch, holding a signal output indicative of the closure independently of the open/close state after that; and logical means, having its input portions connected to the ignition judging means and the closure detecting means and having its output portion connected to the forcible ignition switching means, for turning ON the forcible ignition switching means only when a signal instructing the ignition of the second-stage inflators is outputted from the ignition means, and a signal indicating the closure of the mechanical acceleration switch is outputted from the closure detecting means.
Thus, only if the closure of the mechanical acceleration switch is indicated and the ignition of the second-stage inflators is instructed, the forcible ignition switching means is turned ON and the current from the power supply means is supplied to ignite the second-stage inflators, so the closure of the mechanical acceleration switch must be verified to forcibly ignite the second-stage inflators, thereby preventing false ignition of the inflator due to malfunction of the ignition judging means, and upgrading the safety of the air bag system.
The air bag actuator of this invention includes a one-way conducting element, disposed at the common junction of the first-stage igniting device provided for every one or more first-stage inflators and the second-stage igniting device provided for every one or more second-stage inflators, which are connected in parallel with each other, and passing the current only in one direction, and with respect to the first junction and the second junction which are partitioned by the one-way conducting element at the common junction of the igniting devices, the current is passed only from the first junction to the second junction, and one or more first-stage devices and the mechanical acceleration switch are connected to the first junction, while one or more second-stage igniting devices and the forcible ignition means are connected to the second junction.
Thus, since no current flows into the first-stage igniting device through the forcible ignition means, even if the forcible ignition means malfunctions and the air bags inflate, the air bags inflate within the range limited to the minimum, without igniting the first-stage inflators, thereby upgrading the safety of the air bag system.